1. Field of the Invention
The invention relates to a method and an apparatus for polishing or lapping an aspherical surface of a work piece comprising a tool rotatable about an axis, the working surface area of the tool being smaller than the work piece.
2. Description of the Related Art
In WO 97/00155 A1 there is described a method and an apparatus for optical polishing. The tool used in this method has a flexible working surface and means for selectively varying the pressure applied on the work piece by different regions of the tool working surface. Thereby the effective area of contact between the tool and the work piece can be varied.
The problem of this known apparatus as well as of many other similar apparatus is the complicated and time consuming movement of the tool along the surface of the work piece due to its aspherical shape.
Another apparatus for lapping and/or polishing an aspherical surface is known from EP 0 835 722 A1. The tool used for working the surface is ball-shaped, so that there is only minimal contact between the tool and the work piece, leading to an increase of the operating time.
DE 201 02 684 U1 describes a grinding wheel containing a support made of metal and an outer grinding part containing e.g. diamond as grinding material. Between these two parts there is located a distance ring serving as vibration damper.
Concerning further documents representing the state of the art in the field of polishing or lapping of surfaces using tools, reference is made to JP 09109034 A and JP 09085613 A.
It is an object of the present invention to decrease the time necessary for polishing or lapping the aspherical work piece as well as to increase the accuracy of the process.
This object is solved by an apparatus for polishing or lapping an aspherical surface of a work piece comprising a tool rotatable about an axis, the working surface area of the tool being smaller than the work piece, and an arrangement by means of which the tool and the work piece are adjustable relative to each other in all three directions in space, by means of which the orientation of the tool relative to the work piece is adjustable about at least two axes, and by means of which the work piece is rotatable about an axis.
The advantage of the apparatus according to the invention is its very high flexibility making it possible to adjust and orientate the tool and the work piece relative to one another in six axes, including the axis of rotation of the work piece. This allows the correction of shape defects of the work piece and makes it possible to obtain the exact aspherical surface as necessary. Apart from the higher speed made possible by the invention, the accuracy of the process is also enhanced.
Another aspect of the invention concerns a method of polishing or lapping an aspherical surface of a work piece with a tool rotating about an axis, the working surface area of the tool being smaller than the work piece, adjusting the tool and the work piece relative to each other in all three directions in space, adjusting the orientating of the tool relative o the work piece about at least two axes, and rotating the work piece about an axis.
With this method, work pieces with aspherical surfaces can be polished or lapped quicker and more accurate.
Possible improvements and advantageous embodiments of he invention are given in the dependent claims.